/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if(null == root) {
            return null;
        }
        if(root.val < p.val && root.val < q.val) {
            return lowestCommonAncestor(root.right,p,q);
        }else if(root.val > p.val && root.val > q.val)
        {
            return lowestCommonAncestor(root.left,p,q);
        }else {
            return root;
        }
    }
}